Hydraulic apparatus



March 22, 1966 T. D. H. ANDREWS HYDRAULIC APPARATUS 4 Sheets-Sheet 1 Filed Aug. 28, 1964 F Wm mmw w 8 @m Gt 8 9 3 w E mm mm INVENTOE Thomas D.

H, Andrews ATTORNEY-L? March 22, 1966 T. D. H. ANDREWS HYDRAULIC APPARATUS 4 Sheets-Sheet 5 Filed Aug. 28. 1964 Thomas diiii'iews ATTORNEYS March 22, 1966 T. D. H. ANDREWS 3,241,319

HYDRAULIC APPARATUS Filed Aug. 28, 1964 4 Sheets-Sheet 4.

INVENTOE Thomas D. H. Andrews AT-rolauzvs United States Patent M 3,241,319 HYDRAULIC APPARATUS Thomas D. H. Andrews, Cheltenham, England, assignor to Dowty Technical Developments Limited, Brockhampton Park, near Andoversford, England, a British company Filed Aug. 28, 1964, Ser. No. 392,881) Claims priority, application Great Britain, Aug. 29, 1963, 34,165/63 28 Claims. (CI. 60-53) This invention relates to hydraulic apparatus and more particularly to hydraulic pumps or motors of the til-ting head type. A pump or a motor of the tilting head type comprises a rotary drive member and a head tiltable about an axis, relative to the rotary drive member. The head comprises a casing containing a rotary cylinder block, a rotary drive means between the rotary memher and the cylinder block, and pistons associated with the cylinder block and arranged for reciprocation during rotation of the rotary member. The tilt angle of the head relative to the rotation axis of the rotary member determines the effective stroke of the pistons in their cylinders. A valve means containing a pair of ports is used for the supply and return flow of liquid to and from the cylinders. A pump or a motor of the kind set forth in this paragraph will for convenience be referred to hereafter as a tilting head unit.

The object of the present invention is to provide a compact tilting head unit for use in a hydrostatic power transmission. A further object of the invention is to provide a transmission comprised of tilting head units in which the pistons and cylinder blocks are identical in shape and dimensions and in which the maximum hydraulic capacity of the motor may be cosiderably greater than the maximum capacity per revolution of the pump or vice versa.

In accordance with the present invention, a hydrostatic power transmission includes a pump and a motor hydraulically connected together in which either the pump 'or the motor comprises, or both pump and motor each comprise, a plurality of tilting head units of which the casings are joined together to form one joint casing for tilting movement about one tilt axis and in which the valve means are hydraulically connected together.

Where a transmission has either the pump or the motor but not both arranged as a plurality of tilting head units, the motor or the pump respectively maybe a single tilting head unit.

Where both pump and motor each comprise a plurality of tilting head units or where either the pump or the motor is a single tilting head unit the cylinder blocks and pistons employed in the transmission may be of the same shape and dimensions.

Further, the present invention comprises a plurality of tilting head units arranged with their casings joined to form a joint casing for tilting movement about one tilt axis wherein the drive members are arranged in a housing so that the rotation axis of any one drive member maintains a fixed spaced relationship relative to the rotation axis of any of the other drive members and the cylinder blocks are arranged in the joint casing so that the rotation axis of any one block maintains a fixed space relationship which is the same as the aforesaid space relationship relative to the rotation axis of any other block,

whereby, for any angular setting of the joint casing about the tilt axis, the angular inclination between the rotation axes of the cylinder block and the drive member of any one unit is the same as the angular inclination between the rotation axes of the cylinder block and the drive member of any other unit.

I Preferably, the drive members are mounted for rota- 3,241,319 Patented Mar. 22, 1966 ICC tion about fixed mutually-parallel axes and the cylinder blocks are mounted in the joint casing for rotation about mutually-parallel axes.

The valve means of the units may be hydraulically connected in parallel.

The rotary members of the units may be connected :by toothed gears for rotation at equal speeds.

The present invention also comprises a plurality of tilting head units arranged together so that the casings are comprised by one joint casing mounted for angular movement about one tilt axis, the valve means of the unit being hydraulically connected together and the cylinder blocks being mounted within the joint casing for rotation about mutually-parallel axes.

The rotary drive members may be mounted for rotation in bearings fixed relatively to one another.

The said bearings may locate the drive members for rotation about mutually-parallel axes.

All units of the plurality of tilting head units preferably operate simultaneously either as pumps or as motors.

Five embodiments of the invention will be described with reference to the accompanying drawings, in which:

FIGURE 1 is a detailed cross-section through a joint tilting head motor unit, forming part of a transmission,

FIGURE 2 is a plan view of a valve plate end of the joint head of FIGURE 1,

FIGURE 3 is an elevation of a complete transmission including the motor illustrated in FIGURES l and 2,

FIGURE 4 is a diagrammatic elevation of the transmission of FIGURE 3,

FIGURE 5 is a partial cross-section of a modified form of the motor illustrated in FIGURE 1,

FIGURE 6 is a plan view of a valve end of the joint head of FIGURE 5,

FIGURE 7 is a view partially in section of a further modified form of the motor shown in FIGURE 1,

FIGURE 8 is a detailed view of an isolating valve used in the valve end of the joint head of FIGURE 7,

FIGURE 9 is a diagrammatic elevation of a modified form of the transmission shown in FIGURE 4, and,

FIGURE 10 is a diagramattic elevation of a further modified form of the transmission shown in FIGURE 4 as used for the propulsion of a vehicle. 1

Reference is made initially to FIGURES 3 and 4 of the drawings which show in plan and elevation a hydrostatic power transmission. This transmission corn-prises a tilting head pump unit 1 and a joint tilting head motor unit 2. The pump unit includes a drive shaft 3 adapted to be driven by an engine or other power source and a tilting head 4 whilst the motor unit includes a drive shaft 5 for connection to the load and a joint tilting head unit 6. A pair of parallel links 7 and 8 are pivotally connected between the pump and the motor heads by means of a pair of pivotal connections 9 and 11. The pump 1 is secured in its operative position by means of the bearing housing 12 of the drive shaft 3, this bearing housing being secured against movement in any suitable manner. The tilting head 4 of the pump 1 is mounted for pivotal movement on the bearing housing 12 about the trunnion axis 13. Motor 2 includes a drive shaft bearing housing 14 which is secured fixedly in position by any suitable means. The joint head 6 is secured to the bearing housing 14 for angular movement about the tilt axis 15. The links 7 and 3 include hydraulic flow and return passages for interconnection of the pump with the motor so that rotation of the pump drive shaft 3 displaces liquid through the links 7 and 8 which causes rotation of the motor drive shaft 5.

The tilt axes 13 and 15 and the axes of the pivots 9 and 11 are all parallel one to the other. In the position illustrated in FIGURE 3 the pump head 4 is inthe position corresponding to zero stroke of its pistons, and in this position it is also arranged that the pump tilt axis 13 and the axes of the link pivots 9 and 11 lie in one plane, as the dot-dash line shows. This arrangement gives a dead centre effect in that movement of pump head 4 angularly about the tilt axis 13 from the illustrated position will cause the motor head 6 to move to a position of lesser displacement. In the illustrated position the angular displacement of the motor head 6 is at a maximum value i.e. the piston stroke during rotation of the drive shaft is at a maximum. The geometrical arrangement of the tilting heads and of the link as applied to simple tilting head units is described in detail in United States Patent to Thoma, No. 3,142,963, issued August 4, 1964. Briefly, the adjustment of the pump tilting head 4 from the zero displacement position shown in FIGURE 3 in one direction will displace liquid through the links to the motor to give forward rotation of the motor drive shaft 5 Whilst movement of the pump head in the opposite direction will displace liquid oppositely to cause reverse rotation of the drive shaft 5. As displacement of the pump head increases in either direction from the zero position, the displacement of the motor head will reduce and the speed ratio between the pump and motor drive shafts will therefore increase as pump head displacement is increased.

Reference is now made to FIGURE 1 of the drawings which illustrates in cross-section the motor 2 of FIGURE 3. The motor bearing housing 14 is provided with two sets of bearings 15 and 16 to receive the motor drive shaft 5 and a further shaft 17. Within the housing 14 a cavity 18 is formed which accommodates a pair of toothed gears 19 and 21, which are keyed onto each of the shafts 5 and 17 and which mesh with one another. The two gears 19 and 21 are of equal size so that the shafts 5 and 17 must rotate at equal speeds but in opposite directions.

Extending from the bearing housing 14 are four lugs respectively 22, 23, 24 and 25. The lugs 22 and are located at extreme ends of the bearing housing 14 whilst the lugs 23 and 24 are centrally located. The tilting head 6 comprises a body member 27 and a pair of valve plates 28 and 29 secured by bolts 31 onto the body 27. The body 27 includes a pair of parallel bores 32 and 33 and the central partition 34 between these two bores extends from the body as a lug 35 fitting between the two lugs 23 and 24 of the bearing housing. At either end of the body, lugs 36 and 37 extend in parallel relation with the lugs 22 and 25 of the shaft bearing housing. A pivot pin 38 is secured to the lug 36 for engagement in a cylindrical bore 39 in the lug 22. Similarly a pivot pin 41 is secured to the lug 37 for engagement in a cylindrical bore 42 in the lug 25. A pair of pivot pins 43 and 44 are fixed to the lug 35 to engage in bores 45 and 46 formed respectively in the lugs 23 and 24. All of the bores 39, 42, 45 and 46 are co-axial and the pins 38, 41, 43 and 44 are also co-axial, so that the body 27 and valve plates 28 and 29 may tilt as a unit relatively to the bearing housing 14. In the bore 32 of body 27 a rotary cylinder block 47 is mounted by means of a central fixed pivot pin 48 secured within the valve plate 28 by lock nut 49. Within the cylinder block 47, seven cylinders 51 are formed, each being parallel to the rotation axis of the block 47 and being equally spaced around this rotation axis. From each cylinder 51 a port 52 opens into a flat face 53 of the cylinder block 47. The flat face 53 is in sealing contact with a fiat face 54 of the valve plate 28. Within the flat face 54 a pair of part-circular ports 55 and 56 are located for co-operation with the cylinder ports 52. The shape and extent of these ports may be appreciated in FIG- URE 2.

Within each cylinder 51 a piston 57 is reciprocably mounted. A connecting rod 58 is secured within piston 57 by means of a ball joint 59. The connecting rod extends through a bore 61 in piston 57 which limits the angular movement of the connecting rod within the piston to a small value.

At their outer ends each connecting rod 58 is formeu with a ball joint 62 on which is engaged a slipper 63. In turn the slippers 63 are reciprocably mounted in bores 64 within a drive flange 65. This drive flange 65 is integral with the drive shaft 5 and is located at the inner end thereof. Each slipper includes a flat bearing surface 66 which engages against the flat surface 67 of a wear plate 68 located between the drive flange 65 and the bearing housing 14. Each slipper 63 may in known manner be provided with a recess 60 in its surface 66 which is fed with liquid at pressure from the associated cylinder 51 through a passage within connecting rod 58 for lubrication of the slipper and wear plate surfaces under hydraulic loads exerted on the pistons. Each slipper 63 includes a flange 56 located between the drive flange 65 and the wear plate 68 whose function is to prevent the slipper, connecting rod and piston assembly dis-engaging from the drive flange 65 during outward strokes of the pistons.

Within the bore 33 of body 27 a further cylinder block 71 is mounted for rotation on a fixed pin 72 secured to valve plate 29 by means of locking nut 78. Within block 71, seven equally-spaced cylinders 73 are formed, all be ing parallel to the rotation axis and equally spaced around it. Each cylinder 73 connects with a cylinder port 74 opening into a flat surface 75 of the cylinder block. The flat surface 75 is in rotary sealing engagement with a flat surface 76 of the valve plate 29. Opening into the surface 76 are a pair of arcuate ports 77 and 78 whose shape and position will be more clearly appreciated in FIGURE 2.

Within each cylinder 73 a piston 79 is reciprocably mounted. In a central bore 81 in each piston a connecting rod 82 extends, terminating in a ball joint 83 which connects it to the piston. Bore 81 permits slight angular movement only of the connecting rod within the piston.

The other end of each connecting rod 82 terminates in a ball joint 89 engaging with a slipper 84. Each slipper 84 is reciprocably mounted in a bore 88 formed within a drive flange 86. The drive flange 86 is integrally formed at the inner end of the shaft 17. The slippers each include a bearing surface which bears against a flat hearing surface 98 of a wear plate 87 disposed between drive flange 86 and the bearing housing 14. Each slipper 84 'ncludes a recess 88 in its surface 85 which is fed from the associated cylinders 73 through a passage in the connecting rod to lubricate the slipper surface 85 and to enable it to withstand the hydraulic load exerted on the piston.

Formed on the outer surface of the valve plate 28 is a cylindrical lug 91. A pair of hydraulic passages 92 and 93 open one to each end of the lug 91 and make hydraulic Connection with the pivotal connections 11 of the links 7 and 8. Within the valve plate 28 the passage 92 connects to a hydraulic passage 94 which is in connection with the port 55. The passage 94 extends to one edge 95 of valve plate 28. Also within the valve plate 28 a passage 96 extends from the passage 93 and opens into the edge 95 of the valve plate. This passage 96 makes connection with the port 56 within the valve plate. In the valve plate 29 a passage 97 extends from the port 78 to an edge 98 of the valve plate 29 opposite to the edge 95 of the valve plate 28. A passage 99 also extends within valve plate 29 from the port 77 and opens into the edge 98. The passages 94 and 97 are connected between the edges 95 and 98 by means of a sleeve 181 which fits within the ends of the two passages. Seals in the ends of the two passages ensure that there is no leakage. Similarly the ends of the passages 96 and 99 are connected together by a sleeve 102, seals being provided in the ends of the passages to ensure that there is no leakage.

When the transmission illustrated in FIGURES 1, 2, 3 and 4 is in use the drive shaft 3 of the pump will be driven by an engine or the like. When the pump 1 is in the FIGURE 3 position, it will displace no liquid during rotation of the pump drive shaft 3 and the motor 2 will therefore not move. Assume now that some angular displacein other than their diametrical planes.

ment is given to the pump head 4- so that it will displace the liquid. Further assume that such liquid is delivered through the link 8 to the motor 2 and that the head 6 of the motor as seen in FIGURE 1 is displaced downwardly from the plane of the paper about the axis of the pivot pins 38, 41, 43 and 44, or in other words about the tilt axis 15 (FIGURE 3). Liquid at pressure will then enter the ports 56 and 77 of the valve plates 2% and 29. Such liquid at pressure will then act on pistons of all the cylinders 51 and 73 in connection with the ports 56 and 77. A component of the piston thrust exerted through the connecting rods onto the slippers will react tangentially on the two drive flanges causing them to rotate in opposite directions. Rotation of the drive flanges will move the connecting rods angularly within their pistons to engage the piston bores and thus to apply rotation to the cylinder blocks. The gears 19 and 21 will ensure that the drive flanges rotate in opposite directions at equal speeds. As each cylinder block rotates the cylinders are alternately connected with the two ports in the co-operating valve plate, liquid at low pressure being collected by the two ports 55 and 7S and returned to the pump through the passages 97, 94 and 92. and the link 7.

During rotation of the cylinder blocks and the alternate connection of their cylinder ports to high and low pres sure ports in the valve plates, hydraulic shocks will occur within the liquid in the cylinders following the sudden changes of pressure therein. In the case of a seven cylinder block there will be fourteen such shocks per revolution of the block. These shocks create noise which is difiicult to suppress. The cross-section of FIGURE 1 passes diametrically through one cylinder in each block and if the cylinders were arranged in this relative position the hydraulic shocks occurring in each cylinder during rotation would be simultaneous for the two blocks. other words there would still be fourteen shocks for each revolution of the shaft 5. However, the cross-section of FIGURE 1 is taken purely for convenience in illustration so as to illustrate one piston and cylinder of each block in cross-section. In fact, when the motor is assembled the angular phase relation of the cylinder blocks is such that if a diametrical cross-sectional plane passes diametrically through a cylinder in one cylinder block it will intersect two cylinders in the other cylinder block To put it another way the actual relative phasing of the cylinder blocks is that where one cylinder block operates at a position displaced about thirteen degrees from that illustrated in the drawing. In this way the shocks generated in the cylinders of two cylinder blocks are not simultaneous with one another and it is therefore possible to obtain twenty-eight shocks per revolution. Since the number of shocks is higher and the intensity of each is lower, the problem of silencing the motor when in operation is considerably easier.

Reference is now made to the second embodiment of the invention illustrated in FIGURES 5 and 6. This embodiment comprises a modification of the structure of the motor shown in FIGURES 1 and 2. In FIGURE 5, part of the cross-section of the motor has been shown in outline only and this part is the same as the corresponding part of FIGURE 1. The part of FIGURE 5 actually shown in cross section includes the variation. The variation concerns the arrangement of the gears Within the bearing housing 14-. Where possible, similar reference numerals will be used. The drive shaft 5 extending from .the motor is not connected to the drive flange but it is carried in bearings 105 in the bearing housing centrally between the bearings 15 and 16. The shaft 17 extending from the drive flange 65 is now indicated at 106 and is terminated externally of the bearing housing with lock nuts 107 as is the shaft 17. The chamber 18 within the bearing housing 14 now includes three gear wheels 108, 109, and 111 secured by keys respectively to the shafts 106, 5 and 17. All of these gears are of the same size to ensure that the output shaft 5 rotates at the same speed as the two motor shafts 106 and 17.. It is however, within the scope of the invention to vary the sizes of these gears so that the output shaft 5 may have a predetermined relation other than unity with the speed of the motor shafts. It is of course preferable that the motors should rotate at the same speed and therefore that the gears 108 and 111 should be of the same size.

In the embodiment of FIGURE 1, since only two gears are employed, the two motors will rotate in opposite directions. This requires that the main ports in the valve plates should be connected together in a particular manner which is shown in FIGURES 1 and 2. In the present embodiment the two motors will rotate in the same direction and differing connections of the main ports will therefore be called for. As more particularly shown in FIGURE 6 the main port 78 of valve plate 29 is connected by a passage 112 to the main port 56 of the valve plate 28 and to the connection 93 in the cylindrical lug 91 of valve plate 28. Main port 77 of valve plate 29 is connected through passage 113 with the main port 55 in the valve plate 28 and with the connection 92 in the cylindrical lug 91. A pair of cylindrical sleeves 101 and 102 arranged as shown in FIGURE 2 form parts of the two passages between the two main ports and extend between the adjacent edges and 98 of the valve plates 28 and 29.

In operation of the motor shown in FIGURES 5 and 6, high hydraulic pressure is supplied to one of the two connections 92 or 93. Assume for example that the high pressure is applied to the connection 93. Such high pressure will then be connected to the main ports 56 and 78 in the valve plates 28 and 29 to cause similar rotation of the motors which is transmitted to the output shaft 5 by the gears 108, 109 and 111. The output shaft 5 will of course rotate in the opposite direction to thettwo motors. If the high hydraulic pressure is alternatively supplied to the connection 92 the two motors will rotate in the opposite direction thus reversing the rotational direction of the output shaft 5. The relative phasing of the two motors is arranged in the manner described with reference to FIGURE 1 so as to raise the frequency and reduce the intensity of noise generated.

Reference is now made to the third embodiment of the invention illustrated in FIGURES 7 and8. FIG- URE 7 is a modification of FIGURE 5 and the part thereof shown in outline will be exactly the same as the corresponding part illustrated in FIGURE 1. In FIG- URE 7 the cavity in the bearing housing is provided with three gears 108, 109 and 111 as illustrated in FIG- URE 5 and so arranged that the two motors must rotate in similar directions. One difference from the FIGURE 5 embodiment is that the output shaft 5 is now the shaft which is secured to the drive flange 65 of one motor. The gear 109 is integrally formed on the shaft 114 mounted in bearings 115 for rotation and sliding movement. Externally of the bearing housing a groove 116 is formed peripherally around the shaft 114 for engagement by the pin 117 of a manually-operable lever 11S pivotally secured on bearing housing 14 by means of a lug 119. The chamber 18 in the bearing housing includes an enlargement 121 adjacent to the gear 109 into which the gear 109 may be moved by appropriate movement of the manual control lever 118. When the gear 109 is moved into the space 121 the mechanical connection is broken between the two gears 108 and 111. In particular the motor shaft 17 is new independent of the output shaft 5. The gear 109 is thus used to form a mechanical gear connection to connect the motor shafts 5 and 17 and to also form a clutch capable of disengaging the shaft 17 from the shaft 5.

The purpose of disengaging the motor shaft 17 from the output shaft 5 is to enable on some occasions one motor only to drive the output shaft 5. When it is desired to use one motor only, it is necessary also to disconnect hydraulically the motor of shaft 17 from the hydraulic circuit and this is accomplished by including a shut-off valve between the two valve plates 28 and 29. This valve is illustrated in FIGURE 8 and is intended to fit between the two valve plates in place of two sleeves 101 and 102. The valve comprises a cylindrical body 122 within which a spool valve member 123 is arranged to slide. This valve member includes three lands 124, 125 and 126 spaced by waisted portions. Sleeve connections 127, 128, 129 and 131 extend from the cylindrical body 12 2 and are of such shape and spacing as to fit in the recesses in the edges 95 and 98 of the valve plates 28 and 29 which in FIGURE 6 are occupied by sleeves 1G1 and 102. A spring 132 within the cylinder 122 urges the spool valve 123 to one end of its movement in which the land 124 makes contact with a flange 133 at the opposite end of the cylinder 122. In this position one waisted portion of the spool valve makes a hydraulic connection between the sleeves 127, 128 and the other waisted portion makes hydraulic connection between the sleeves 129 and 131. Thus in the position as shown in FIGURE 8, the two motors in FIGURE 7 will be connected together in the manner shown in FIGURE 6. For operation of the valve of FIGURE 8, an external mechanism is provided. This comprises a shaft 134 mounted externally of the body 27 of the casing by means of a pair of brackets 135, a lever 136 secured to one end of the shaft 134 which terminates adjacent to an operating projection 137 extending from the spool valve 123, and a lever 138 at the opposite end of the shaft 134 which extends to a position adjacent to the tilt axis of the casing 27. Externally of the motor in a rigidly supported bracket 139 a plunger 141 is mounted which carries at one end a. frusto-conical cam 142 which co-operates with the lever 138. The plunger 141 is adapted for manual operation and when it is moved towards the casing 27 it causes angular movement of the lever 138, the shaft 134, and the lever 136 to depress the spool valve member 123 in its cylinder, thus moving the lands 124 and 125 to shut off flow between the sleeves 127, 128, 129 and 131. If the plunger 141 is retained depressed it will hold the valve member 123 depressed against its spring loading irrespective of the angular position taken up by the head 6 about its trunnion axis.

The motor of FIGURES 7 and 8 is intended to be used in the transmission of FIGURES 3 and 4 and in the condition where plunger 141 is not depressed and the gear 109 interconnects the two motors, the operation of the motor will be exactly as described with reference to FIGURES and 6. However, if desired to use only one motor to rotate the output shaft 5 the lever 118 is moved to disengage the gear 109 and the plunger 141 is depressed to close the valve between the two motors. In this case only the motor formed by the drive flange 65 and the cylinder block 47 will drive the output shaft 5. The advantage gained by this arrangement is that the output obtained from the drive shaft 5 is at a higher speed and lower torque. In fact this arrangement doubles the effective range of speed ratio variation of the transmission. With the illustrated gear arrangement of FIGURE 7, it is not possible to maintain the desired phase relation between the two motors after disengagement and re-engagement of the gear 109 unless it is arranged that the two gears 1G8 and 111 each have fourteen teeth i.e. twice the number of cylinders in each cylinder block. In this case the relative phasing can be maintained.

In the embodiment of FIGURES 1 to 4, the cylindrical lug 91 by which hydraulic connection is taken to the motor, has been shown secured to one valve plate only and is thus located to one side of the motor unit. With this arrangement the pump drive shaft 3 may either be completely aligned with the motor output shaft 5 or may be spaced from it transversely a substantial distance. An alternative arrangement forms another embodiment illustrated in FIGURE 9. In this case the cylindrical lug 91 is secured jointly between the two valve plates on the motor head 6 so as to occupy a position approximately mid-way between the two motor shafts. By this arrangement a small transverse spacing may be provided between the two motor shafts.

The fifth embodiment of the invention is illustrated in FIGURE 10. In this embodiment the gears are omitted between the two drive shafts 5 and 17 of the two motors. Other than this the arrangement of the motors is exactly as described in FIGURES 1 and 2. The drive shaft 5 at its outer end carries a bevel gear 151 which meshes with co-operating bevel gear 152 mounted on a half shaft 153 of the vehicle. This half shaft directly connects to the ground-engaging wheel 154. The motor drive shaft 7 at its outer end carries a bevel gear 155 which meshes with the co-operating gear 156 mounted on a half shaft 157. The half shaft 157 is directly connected to another wheel 158 of the vehicle. The two half shafts 153 and 157 are inwardly extended from bevel gears 152 and 156 into a dog clutch unit 159 capable of locking the shafts 153 and 157 together if desired. The pump drive shaft 3 is connected for driving by the vehicle engine. The pump and motor heads 4 and 6 are connected by links 7 and 8 arranged as described with reference to FIGURES 3 and 4. The relative angular displacement taken up by the joint motor head will determine the speed ratio of the transmission between the pump drive shaft 3 and the two motor shafts S and 17. With the dog-clutch 159 unlocked and the main ports in the motor valve plates connected in parallel in the manner shown in FIGURE 1, it will be seen that a differential effect may be obtained between the two motor drive shafts 5 and 17 in that the two shafts may rotate at different speeds, but the total rotation over any period of time for the two motor drive shafts will be proportional to the quantity of liquid pumped to the motors by the pump 4 in that period. Thus in the arrangement shown the parallel connection between the main ports of the two valve plates will permit differential action to take place between the two ground engaging wheels 154 and 158. In the event that it is desired to dispense with the differential action, the clutch 159 may be engaged. The two wheels 154 and 158 will then rotate as one unit and the driving speeds of the two drive shafts 5 and 7 will be exactly similar.

In all the described embodiments of the invention, the pump 1 is a conventional tilting head pump unit having only one rotary cylinder block. Preferably this cylinder block is provided with pistons which co-operate with the drive flange and the pump drive shaft in exactly the same manner that one motor cylinder block oo-operates with its drive flange and its drive shaft. Advantage is obtained in any of the transmisisons illustrated both in manufacture and in subsequent servicing during use if the pump and motor cylinder blocks, pistons, connecting rods and slippers are of identical shape and dimensions. More particularly, advantage is obtained in the servicing of transmissions since spare cylinder blocks, pistons, connecting rods and the like are equally usable in both pumps and motors. In this described embodiment, the use of one pump which is parallelly connected to two motors of the equivalent dimensions gives a range of transmission speed ratios which is very convenient for vehicle propulsion. The described embodiments show two tilting head units mounted with their heads secured together for joint tilting movement about one tilt axis. It is however, wlthin the scope of the invention to provide three, four or possibly more units with their heads secured together for joint tilting movement.

In the described embodiments the joint units have been provided only to act as motors. It is however within the scope of the invention to arrange a joint unit to act as a pump. It is also within the invention to arrange a joint unit to act as a complete transmission, for example, a construction combining two tilting head units in which the cylinder block rotation axes in the joint casing are parallel, the rotation axes of the drive members are nonparallel and the drive members are connected to receive and to deliver power. In such a case, the adjustment of the joint head about the tilt axis will vary the speed ratio of hydraulic energy translating devices hydraulically connected together in which at least one of these devices comprises a plurality of tilting head units of which the casings are joined together to form one joint casing within which the cylinder blocks are rotatable about mutually parallel axes, and in which the valve means are hydraulically connected together.

2. A hydrostatic power transmission as claimed in claim 1, wherein the motor is a tilting head unit and including a link pivotally connected to both pump and motor heads at positions spaced from the tilt axes so that pump and motor heads must move jointly about their tilt axes for adjustment of the piston strokes.

3. A hydrostatic power transmission as claimed in claim 1, wherein the pump is a tilting head unit and including a link pivotally connected to both pump and motor heads at positions spaced from their tilt axes so that the pump and motor heads must move jointly about their tilt axes for adjustment of their piston strokes.

4. A hydrostatic power transmission as claimed in claim 1, including a link pivotally connected to both pump and motor heads at positions spaced from their tilt axes so that pump and motor heads must move jointly about their tilt axes for adjustment of their piston strokes.

5. A hydrostatic power transmission as claimed in claim 3, wherein the link includes a hydraulic passage forming part of the hydraulic connection beween the pump and the motor.

6. A hydrostatic power transmission as claimed in claim 4, wherein the link includes a hydraulic passage forming part of the hydraulic connection between the pump and the motor.

7. A hydrostatic power transmission as claimed in claim 3, wherein the link is capable during adjustment of the tilt angles of the pump and the motor heads of passing through a dead centre position where its pivots lie in a plane passing through the pump tilt head axis, this dead centre position being arranged to determine the maximum tilt angle of the motor head.

8. A hydrostatic power transmisison as claimed in claim 4, wherein the link is capable during adjustment of the tilt angles of the pump and the motor heads of passing through a dead centre position where its pivots lie in a plane passing through the pump tilt axis, this dead centre position being arranged to determine the maximum tilt angle of the motor head.

9. A hydrostatic pouver transmission as claimed in claim 7, wherein the dead centre position of the link is arranged to coincide with the zero stroke position of the pump head.

14). A hydrostatic power transmisison as claimed in claim 8, wherein the dead centre position of the link is arranged to coincide with the zero piston stroke position of the pump head.

11. A hydrostatic power transmission including a pump and a motor hydraulically connected together, the motor comprising two tilting head units, each having a casing joined to the other casing to form one joint casing for tilt movement about one tilt axis, valve means joining the two casings in parallel, and a pair of shafts extending independently from and driven one from each unit, to drive individual loads.

12. A vehicle including a hydrostatic power transmission as claimed in claim 11, including a disconnectible clutch capable of connecting together, or disconnecting at will the two independent shafts.

13. A plurality of tilting head units arranged with their casings joined to form a joint casing for tilting movement about one tilt axis wherein drive members are arranged in a housing so that the rotation axis of any one drive member maintains a fixed spaced relationship relative to the rotation axis of any other drive member, and cylinder blocks are arranged in the joint casing so that the rotation axis of any one block maintains a fixed spaced relationship, which is the same as the aforesaid spaced relationship, relative to the rotation axis of any other block, whereby, for any angular setting of the joint casing about the tilt axis, the angular inclination between the rotation axes of the cylinder block and drive member of any one unit is the same as the angular inclination between the rotation axes of the cylinder block and drive member of any other unit.

14. A plurality of tilting head units as claimed in claim 13, wherein relatively fixed bearings are arranged to locate the drive members for rotation about fixed mutuallyparallel axes, and the cylinder blocks are mounted in the joint casing for rotation about mutually-parallel axes.

15. A plurality of tilting head units as claimed in claim 13 wherein valve means of the unit are connected in parallel.

16. A plurality of tilting head units as claimed in claim 1 wherein valve means of the tilting head units are hydraulically connected in parallel.

17. A plurality of tilting head units as claimed in claim 13, including toothed gears secured to the rotary members and intermeshing to ensure that the rotary members notate at equal speeds.

18. A plurality of tilting head units as claimed in claim 17 wherein a drive shaft extends from one rotary member to form the power transfer connection for all rotary members.

19. A plurality of tilting head units as claimed in claim 17, including a drive shaft extending from a toothed gear which is connected only to the rotary members by the meshing of the toothed gears.

20. A plurality of tilting head units as claimed in claim 17 wherein a clutch is arranged to disconnect the rotary member of one tilting head unit from the toothed gears and hydraulic disconnecting means to isolate the cylinder block of the unit hydraulically.

21. A plurality of tilting head units as claimed in claim 13, wherein the joint casing comprises a body member having a plurality of bores one for each cylinder block, a valve plate for each bore for co-operating with the associated cylinder block, at least two lugs extending from the body, a bearing housing for the drive members, at least a pair of lugs extending from the bearing housing, and pivot pins pivotally connecting the lugs together to facilitate tilt movement of the joint heads on the bearing housing about the tilt axis.

22. A plurality of tilting head units as claimed in claim 21, wherein the bores in the body are located so that their axes lie in one plane with the tilt axis, each bore axis being perpendicular to the tilt axis, and including a lug extending from the body between each adjacent pair of bores for attachment by a pivot pin to a corresponding lug extending from the bearing housing, all the pivot pins being co-axial with the tilt axis.

-23. A plurality of tilting head units as claimed in claim 17, wherein the gears are arranged to give a phase relationship between the rotation of the blocks such that the angular position of one block at which a cylinder moves from one main port to the other of the valve means does not coincide with the angular position of another block at which a cylinder moves from one main port to the other of its valve means.

24. A plurality of tilting head units as claimed in claim 23, wherein the plurality comprises two tilting head ill units only, the cylinder block of each unit having an odd number N of cylinders and wherein the phase relation between these cylinder blocks is 360/ 4N degrees.

25. A plurality of tilting head units arranged together so that the casings comprise one joint casing mounted for angular movement about one tilt axis, valve means of the unit being hydraulically connected together and cylinder blocks being arranged within the casing for rotation about mutually-parallel axes.

26. A plurality of tilting head units as claimed in claim 25, wherein the rotary drive members of the units are mounted for rotation in bearings fixed relatively to one another.

27. A plurality of tilting head units as claimed in claim rotation about mutually-parallel axes.

References Cited by the Examiner UNITED STATES PATENTS 2,981,068 4/1961 Foerster et a1. 60--53 3,074,296 1/1963 Ebert 6053 X 3,123,975 3/1964 Ebert 6053 3,142,963 8/1964 Thoma 60-53 3,143,859 8/1964 Thoma 60-53 GEOHEGAN, Primary Examiner. 

1. A HYDROSTATIC POWER TRANSMISSION COMPRISING A PAIR OF HYDRAULIC ENERGY TRANSLATING DEVICES HYDRAULICALLY CONNECTED TOGETHER IN WHICH AT LEAST ONE OF THESE DEVICES COMPRISES A PLURALITY OF TILTING HEAD UNITS OF WHICH THE CASINGS ARE JOINED TOGETHER TO FORM ONE JOINT CASING WITHIN WHICH 